The source code is maintained in a Visual Studio 2008 environment, with WSPBuilder Version 0.9.9.0728.

After adding the WSP to your SharePoint environment, and deploying it, a Web Application feature will appear that must be activated on any web app on which users customise SharePoint Designer Workflows. If the feature isn't activated, users who open the
SharePoint Designer Workflows UI will encounter an error when loading the SharePoint Designer Workflow UI. The error can be ignored, however none of these custom Workflow Actions will be available as a result.

After the feature is activated, you will see a bunch of new Workflow Actions in SharePoint Designer. Find them in the Workflow Designer by selecting the "Actions" drop-down button, choose "More Actions..." then choose "String Actions"
from the "Select a Category" drop-down.

There is one known issue for this release:

The Web Application feature does not de-activate itself correctly. To back-out the change made by the Web Application feature, you can manually edit the web app's web.config, and remove the <authorizedType> where the Assembly attribute equals
"SPDWorkflowStringActions, Version=2.0.0.0, Culture=neutral, PublicKeyToken=3825586d873cffa1"